1. Field of the Invention
The subject invention relates to information recording and, more specifically, to multistyli recording systems, printer-plotters and apparatus capable of printing gray tone graphical and picture information as well as line graphics and alphanumerical characters. The invention also relates to digital facsimile receivers.
2. Prior-Art Statement
Reciprocating facsimile apparatus have been known for a long time, as may, for instance, be seen from U.S. Pat. No. 2,311,803, by R. J. Wise et al, employing a flying pen or stylus. Some systems have attempted to dispense with the need for a stylus drive by arranging a series of stationary styli across the recording medium or paper, as may, for instance, be seen in U.S. Pat. No. 2,937,064, by D. A. Walsh. In practice, stationary recording styli impose a severe limit to attainable resolution.
Some prior-art proposals have attempted to overcome such and other drawbacks by providing moving styli or stylus assemblies with the aid of endless bands, as may, for instance, be seen in U.S. Pat. No. 3,166,752, by H. C. Waterman, U.S. Pat. No. 3,369,250, by T. H. Gifft and French Pat. No. 1.349.168, by A. Hermet. In an effort to overcome design and performance limitations of such endless belt systems, a multistyli system of the type shown, for instance, in British Pat. No. 943,011 has been developed. In particular, this British patent discloses an electrically controlled character printer which prints using a plurality of styli, each stylus printing one character in a line of characters. The styli are oscillated by an amplitude equal to the stylus spacing and equal to the width of characters to be printed. At the same time the record sheet is continuously moved in a direction at right angles to the line of styli so that each character is built up over a plurality of stylus oscillations with the styli being activated at proper points within the oscillation cycle to produce a character formed by a number of print dots resulting from the stylus striking an ink ribbon disposed between the styli and the record sheet or formed by such other known ways as Xerography. As a matter of interest, recording systems in which the lateral deflections of styli are limited to interstylus spacing are disclosed in German Pat. No. 936,582, by J. Dreyfus-Graf.
U.S. Pat. No. 3,644,931, assigned to the subject assignee and herewith incorporated by reference herein, discloses a multi-styli recorder where the styli are again oscillated transverse to the record sheet motion to effect marking by electric discharges through an electro-sensitive record sheet. Each stylus prints within an assigned band as the record sheet is continuously advanced. The multichannel recorder disclosed produces a record with information displayed as a print intensity modulation which may vary down each band and between bands.
Variation in print intensity is achieved by varying the styli discharge pulse rate so that high print intensities are achieved with a high pulse rate and thus pulse density. The pulse rate of each stylus is varied in accordance with the usually analogue signal applied to each of the recorder channels.
Patterson, Ruffell, Walker and Schwartz in "A Digital Input Picture Printer System", a paper presented at the National Electronics and Geophysics Convention at the University of Auckland, August 1974, have described a printer capable of printing alpha-numerica characters and gray tone graphics and pictures which was developed from the multistyli recorder of the latter U.S. Pat. No. 3,644,931. The printer disclosed by Patterson et al prints each line of information as a series of dots, the size-intensity of which are determined by the styli writing pulse length and each line is printed while the styli are oscillated in a left to right direction with an amplitude equal to the styli spacing. The styli printing information is accepted and stored for the subsequent line as the styli are oscillated in a right to left direction during which time the electro-sensitive record sheet is advanced by a predetermined line spacing distance.
With the latter type of equipment, a certain printing speed increase may be brought about by increasing the stylus reciprocation frequency. However, practically attainable speed increases are limited by such factors as vibration and mechanical load on the stylus drive due to the mass of the stylus head and reciprocation assembly. Such factors increase as the square of the stylus reciprocation frequency, imposing thereby a natural limit that can only be overcome by a radically new approach.